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I received a phone call last week from the publisher of the OU journal "Torah Tidbits". He had seen my post on the upcoming total eclipse of the moon and had discovered some interesting halachic intricacies having to do with saying Kiddush Levana (the blessing of the moon) in a month with a total lunar eclipse.
Usually one can say Kiddush Levana as long as the moon is waxing, including the entire night of the full moon. However an interesting exception comes into play when a total lunar eclipse occurs. The exception is as follows: If one personally witnesses the total lunar eclipse, and if one understands what a total lunar eclipse means, i.e. that the moon has reached its fullest light, then as soon as the eclipse begins, one can no longer say Kiddush Levana.
The intriguing part of this halacha is that BOTH conditions must apply. One must both experience the eclipse and know what it means. If either condition alone applies, then one can continue to say Kiddush Levana the entire night. It is unusual for both the experiencing of an event and an understanding of it to be required in halacha. For example, Pesach begins at a certain time, whether or not one experiences the full moon of Nissan or even knows what it means.
I hope I have conveyed this correctly. If not, all of the errors are mine.
(Caution: I am not a Rabbi or a halachic authority.) :)